A known system detects that a user is present at a predetermined range of surroundings of a vehicle, or that the user being on the vehicle gets off, by, for example, a communication device communicating with a mobile device that is possessed by the user. In a case where the system detects that the user is present at the predetermined range of the surroundings of the vehicle, the system automatically unlocks a door of the vehicle. In a case where the system detects that the user gets off the vehicle, the system automatically locks the door of the vehicle.
A known bar antenna, which is an example of the communication device of the system, is disclosed in JP4655230B (hereinafter referred to as Patent reference 1). The bar antenna disclosed in Patent reference 1, the bar antenna being mounted to a door handle of the vehicle, serves as a transmission antenna transmitting signals to the mobile device of the user and includes a pair of bobbins that holds respective end portions of a stick-shaped core. A conductive wire is wound around the core that is held by the pair of bobbins to form a coil.
A dimension of the bar antenna in a longitudinal direction can be short by reducing the dimension of the core in the longitudinal direction. Meanwhile, the region of the core around which the conductive wire can be wound is reduced as the length of the core is reduced. Thus, in a case where the length of the core is reduced, the number of windings of the conductive wire is reduced. Accordingly, the inductance desired for the coil may not be secured.
In order to solve this problem, the conductive wire is laminated to be wound around the core, for example. In a case where this solution is applied to the core disclosed in Patent reference 1, a first layer of the conductive wire is wound from a first bobbin that holds the core to a second bobbin that holds the core. Then, the conductive wire is turned back at the second bobbin and a second layer of the conductive line is wound. However, a turned-back portion of the conductive wire is pulled to a side where the first bobbin is positioned in accordance with the winding of the second layer of the conductive wire. Accordingly, an irregular shape of winding of the conductive wire may occur.
A need thus exists for a bobbin for a bar antenna and the bar antenna including the bobbin which is not susceptible to the drawback mentioned above.